Ya im a server admin and we have 4 servers up of it already. It actually plays fairly smoothly. Considering most of the game is AI(BOTS) which usually take heavy cpu resources and memory on the server side, this game seems to be fairly well optimized.
On client side, you shouldnt need to crazy of a rig to play it. 8800GT is plenty. Im sure a 7800GT or even lower would play it fine.
The only downside is valve kinda screwed up with how they did the server menus and crap. Like there is no server browser yet, it doesnt currently work like most every other game. Currently it is a matchmaking system that just sticks you randomly onto a server which "supposedly" you ping good to, which doesnt always happen either. You cant pick a server in a browser to join yet. This is what alot of people are really angry about. There will be many many patches coming soon for this game, just fyi.